Schwartzschildt effect

[Stanee Rae Pettit Murray <stanee-rae@xxxxxxxxxxxxxxxx>]

Willem-Jan Markerink wrote:

>> Could you give us a brief lecture on Schwarzschildt effect? ;-)
>
>I was hoping noone would ask....it might be opposite to the original 
>problem: AFAIK, Schwarschildt discovered that long exposures need 
>additional time to get the same results as was calculated. Caused by 
>slower acting film when few photons hit the film. I am not 
>sure if this phenomena equals the requirement of *less* exposure at 
>very short shutter times, I somehow feel it should also require more 
>exposure than calculated.
>
 
I've never heard of the Schwarzschildt effect, but by previous discussions I
figured out what you meant.  I've only heard it called Reciprocity Failure.
This description comes from "Photography," 5th edition, by London & Upton:

"The reciprocity effect occurs at exposures of one second or longer (and at
exposures shorter than 1/1000 second).  You get a decrease in effective film
speed and consequently underexposure.  To make up for the decrease in film
speed, you must increase the exposure.  The exact increase varies with
different types of film.  The reciprocity effect in color films is more
complicated, since each color layer responds differently, changing the color
balance as well as the overall exposure."

They give a chart for b&w films, showing the changes necessary for
increasing the exposure (by aperature or shutter speed) and changes in
development time.  But infrared isn't listed.

This book was recommended to me as an authority on photography, and the
"manual" I needed in order to study for the CPP (certified professional
photographer) exam.

Stanee


Stanee Rae Murray, CPP, owner
Stanee Rae Studio
<stanee-rae@xxxxxxxxxxxxxxxx>
voice phone (908) 842-5268


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Topic No. 3